In a plasma process for manufacturing semiconductor devices or liquid crystal displays, high frequency wave or microwave is used to electrically discharge or ionize a processing gas in a vacuum processing chamber. As for a high frequency discharge method, a capacitive coupling type plasma processing apparatus is mainly used, in which a pair of electrodes is disposed with an adequate gap in parallel such that one electrode is grounded and the other electrode is applied with high frequency wave for producing plasma. However, the high frequency discharge method has some problems in that it is difficult to produce high-density plasma at a low voltage, as well as devices on the surface of the substrate may be easily damaged because of a high electron temperature. In that respect, a microwave discharge method is advantageous in that high-density plasma having a low electron temperature may be produced at a low voltage. In particular, plate-type surface wave plasma (SWP) has an advantage in that large-diameter plasma may be generated efficiently in a wide pressure range, and magnetic field is not needed, thereby facilitating simplification of the plasma processing apparatus.
In the microwave discharge type plasma processing apparatus, particularly, a plasma etching apparatus, an RF electrode is placed at a relatively low position in a processing chamber, a substrate to be processed, for example, a semiconductor wafer is fixed thereon, plasma is generated above the RF electrode by microwave discharge to expose the surface to be processed (upper surface) of the wafer to a reactive radical in the plasma, and high frequency wave for RF bias is applied via a blocking condenser to the RF electrode to draw ions in the plasma onto the surface to be processed of the wafer by a self-biased voltage generated in the RF electrode (see, e.g., Patent Document 1).